The present invention relates to a display device including a charging section dc-wise connected to a commercial power source and a non-charging section dc-wise isolated from the commercial power source, and more particularly to a display device in which a leakage current generated between the charging section and the non-charging section is reduced.
A display device having a Braun tube (or CRT) is provided with a flyback transformer which generates a high anode voltage and a deflection yoke which includes a vertical deflection coil and a horizontal deflection coil. In such a display device, in order to eliminate an insulating type of power source transformer which effects a dc-wise isolation from a commercial power source, a drive transformer to drive a horizontal output circuit and the flyback transformer are utilized so that only the horizontal output circuit generating a high voltage is dc-wise connected with the commercial power source while the other circuits are dc-wise insulated from the commercial power source. A primary winding and a secondary winding of the flyback transformer are coupled by a capacitance formed therebetween. Therefore, a leakage current flows from the secondary winding (or non-charging section) toward the primary winding (or charging section) due to a potential difference between a flyback pulse generated at the primary winding and a flyback pulse generated at the secondary winding. On the other hand, since the horizontal deflection coil and the vertical deflection coil are arranged in proximity to each other at a neck portion of the CRT, a leakage current flows from the horizontal deflection coil (or charging section) toward the vertical deflection coil (or non-charging section). Also, between wirings or conductor patterns of a printed board may exist a leakage current which flows from the charging section toward the non-charging section due to a capacitive coupling depending on a potential difference. A conducting path which connects the ground point of the charging section and the ground point of the non-charging section with each other, is formed by the commercial power source and the ground point of an external device (for example, VCR or audio device) connected to the display device. A total value of those leakage currents should be not larger than 1 mA RMS in accordance with the Japanese law for the control of electric articles and not larger than 0.5 mA RMS in accordance with the UL standard of U.S.A. However, in a stacked or laminated-layer winding type of flyback transformer as disclosed by, for example, JP-A-No. 51-20307 or U.S. Pat. No. 3,381,204, there may be the case where the above-mentioned standards cannot be satisfied since a relatively large leakage current due to a capacitive coupling flows in the first layer of a secondary winding, one end of which is connected with a +B line directly (or through no diode).